Epidemiological data published in the American Journal of Clinical Nutrition by Theodore Brasky and his team from The Ohio State University suggested that there was an association between high omega-3 intakes and an increased risk of endometrial cancer in overweight and obese women.
On the other hand, increased intakes of omega-3s for normal-weight women were associated with statistically significant reductions in cancer risk, said the researchers.
The only other study examining specific omega-3 intakes and endometrial cancer was performed by Hannah Arem et al. from Yale School of Public Health, which found that high intakes of omega-3s may reduce the risk of this particular cancer (European Journal of Nutrition, 2013, Vol. 52, pp. 1251-60. doi: 10.1007/s00394-012-0436-z).
However, other studies examining fish intake and endometrial cancer have found a positive association.
Commenting on the study’s findings, Harry Rice, PhD, V.P., Regulatory & Scientific Affairs for GOED, told us: “While results from this study may provide a reason to conduct further research at some point in time, they do not support a change (increase or decrease) in omega-3 intake.”
That prostate cancer study
The study’s findings may attract attention since the authors, Brasky et al., were also involved in last year’s controversial prostate cancer study. That study has been widely debated in omega-3 circles, with many taking exception to the conclusions.
Indeed, the prostate cancer study, which was published in the Journal of the National Cancer Institute (doi: 10.1093/jnci/djt174), was also epidemiological and again showed correlation and not causation. It also only measured blood levels of omega-3s and did not consider any differences between fish and supplements. Despite this, co-author Dr Alan Kristal from Fred Hutchinson Cancer Research Center, USA, stated: “We've shown once again that use of nutritional supplements may be harmful.”
For the new study, Dr Brasky and his co-workers examined intakes of long-chain omega-3s, including EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) in 22,494 women aged between 50 and 76 living in Washington State. Intakes from the diet and supplements were assessed using a semi-quantitative food-frequency questionnaire (FFQ).
Over nine years of data collection, there were 263 cases of endometrial cancers documented.
Results showed that women with the highest average dietary intakes of EPA + DHA (over 256 mg per day) had a 79% increased risk of endometrial cancer, compared to women with the lowest average intakes (less than 60 mg per day). Further number crunching showed that the increases in risk were restricted to overweight and obese women, whereas statistically significant reductions in risk were observed for normal-weight women.
“When supplemental exposures were considered in addition to diet, the findings were similar,” added Dr Brasky and his co-authors.
“In this large prospective study, we found that intake of long-chain omega-3 PUFAs and their food sources are positively associated with endometrial cancer risk among overweight and obese women,” they wrote. “In normal-weight women, long-chain omega-3 fatty acids may provide some benefit.
“Because this is an observational study, replication in randomized trials is necessary to confirm these findings. One such study, the ongoing VITamin D and Omega-3 TriAL (VITAL), may be helpful in verifying the results we report here.”
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi:10.3945/ajcn.113.070524
“Associations of long-chain omega-3 fatty acids and fish intake with endometrial cancer risk in the VITamins And Lifestyle cohort”
Authors: Theodore M Brasky, Marian L Neuhouser, David E Cohn, and Emily White